# Tagged Questions

C is a general purpose programming language. Originally intended for implementing system software, C and its close relatives are the principle languages used in most modern operating systems. Due to its thin layer of abstraction and low overhead, C allows efficient coding of algorithms and data ...

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### Open Source Linear Algebra Library

I am making a code in C that requires the equivalent of Matlab's '\' command for a linear system of the form AX=B where A is an NxN matrix and X, B are Nx1 vectors- i.e a code that performs X=A\B that ...
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### Array initialization in C

In this bit of code, the X and Y arrays should be identical but for some reason, that I CANNOT figure out for the life of me, X[0] is always 1 rather than 0. I have tried initializing the whole array ...
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### Error in MD simulation with Lennard-Jones potential in C, resulting in a lack of conservation of energy

I'm working on a MD simulation using the Lennard-Jones potential and the Velocity Verlet algorithm. The code compiles and runs, but the energy for each time step is not conserved; it decreases ...
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### Implementing velocity verlet for harmonic oscillator in C gives error wrt conservation of energy

I'm attempting to implement velocity Verlet with a harmonic oscillator in C, but I have some errors: Energy is not being conserved Energy oscillates much more than I would expect I believe the ...
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### Simulation of Parabolic Cylinder Function $U(a,x)$ for complex arguments

According to Wolfram Mathworld $U(a,x) = D_{-a-1/2} (x),$ and $D_v(z) = 2^{v/2}e^{-z^2/4}U(-\frac{1}{2}v, \frac{1}{2}, \frac{1}{2}z^2)$, Using the GNU Scientific Library (GSL) it seems possible ...
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### Pivoting in Crout algorithm

Consider the following code, found on wikipedia, that implements the Crout decomposition algorithm: ...
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### What PRNG function is this?

This is a 16-bit PRNG function, transcribed from assembly to C for easier reading: ...
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### PETSc - difference between PetscNew and PetscMalloc

I wonder what is the difference between both functions. In C++, the difference between new and malloc is easier: new allocates memory by calling the constructor. What about PETSc ? In the example, ...
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### PETCs - How should one initialize PetscRandom?

The documentation of PETSc shows an example of usage: ...
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### Implementing std::nextafter: Should denormals-are-zero mode affect it? If so, how?

This might be the wrong stackexchange site for this question. math.SE, cs.SE, programmers.SE, and of course stackoverflow are all possibilities. I'm hoping to reach an audience that might actually ...
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### Indexing Nested Loops in C [closed]

I am having trouble indexing correctly the below statement in C inside a function and then returning it as a pointer. The returning part should not be confusing - hopefully - however the indexing is a ...
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### Programming language for HPC [closed]

I'm planning on building a program that will carry out HPC. I'm aware that C/C++ is significantly better than Python in terms of the speed of computation. However, I'm not yet proficient in C/C++, so ...
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### How to build a regression tree in C++

I want to build a random forest that estimates facial landmarks. A random forest is a set of regression trees, built in a certain way. The problem is that I am new to machine learning, yes I ...
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### Kummer's confluent hypergeometric for complex arguments in C/C++?

I need to evaluate Kummer's confluent hypergeometric function for imaginary arguments: $$_1F_1(a,b;ix)$$ where $i$ is the imaginary unit, $a,b,x$ are real, and $a,b>0$. Is there a routine ...
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### Do BLAS routines compute their respective operations with minimum error?

Do all BLAS routines compute the respective operation with minimum error ? i.e. Is the reduction in sdot computed with least error ? I need to call these ...
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### solver linear system equation

I need to solve to solve a "large" symmetric sparse linear systems, with matrix size 8000? I heard about HSL, ITPACK, but I don't know how to use them, and I am working in C language.
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### Use of structs in Axisymmetric Finite Volume method

This might be better somewhere else, but I'll give it a try here first. I'm implementing a finite volume scheme for an axisymmetric problem in C, and am looking for a more efficient way to handle all ...
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### Profiling optimized C code using gprof

I have a simple C code with many function calls, which I profiled using gprof. ...
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### Kronecker products and basis contractions (ie. B.A.Transpose[B]) in C?

I have implemented a basis transformation in C of the following form kron[A,A]*B*Transpose[kron[A,A]] where A and ...
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### Recommendation for C/C++ library which offers Schur complement functions?

I need to find C/C++ libraries which offer function for computing Schur complement. I know about MUMPS and Pastix, but I need more of them to compare them in my research. Do you have any experience ...
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### What is wrong with this matrix multiplication?

I am attempting to write a matrix multiplication routine because I need to do some analysis in CUDA and I want to validate it with CPU code. I am trying to use <...
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### BLAS, LAPACK or ATLAS for Matrix Multiplication in C

I am trying to find the most optimized way to perform Matrix Multiplication of very large sizes in C language and under Windows 7 or Ubuntu 14.04. And searching led me to BLAS, LAPACK and ATLAS. ...
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### Water Properties IAPWS-IF97 implementation on C/C++

I'm Looking for an implementation of the IAPWS-IF97 water properties on C/C++. I'm aware of the library freesteam. However freesteam does not include all the properties I'm looking for. Particularly I ...
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### Ways to solve numerically differential equations in C [closed]

I have to solve numerically a differential equation in C. The equation is: How can I write some code to solve it? Are there some numerical methods (Runge-Kutta maybe?) to solve it? A colleague ...
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### Elemental vs DPLASMA

I want to use one of these two libraries into my C++ project to basically invert a dense matrix (with Cholesky). Of course, I am interested in a distributed environment. Both libraries seem nice so ...
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### Find area of a polygon. In C and Obj C.

I've been given an assignment: Create a console application (using C and Obj C) that will calculate area of a random polygon. The application should process input data as a .txt file with a list of ...
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### Is it valid MPI-3 to nest non-blocking collectives?

Is the following a standards-conformant MPI-3 C program? ...
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### How to change one bit of a 32 bit integer in C

I have three 32 bit integers a,b,c. I want to make 10th bit of a=(23 rd bit of b) xor (4th bit of c) without disturbing other bits of a. How can I do this in C programming language? a can be zero ...
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### Efficient compressed row storage Gauss Seidel C/C++

I am trying to figure out why my sparse (CRS) Gauss Seidel solver is so slow. I tried to find an implementation of the Gauss Seidel method in sparse format online but could only find implementations ...
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### Use of Java or Scala in HPC?

I was looking to brush up and/or pick up some languages for a hobby project on my free Amazon EC2, and I was going through the benchmark results for Java vs C (or Scala vs C)and Fortran vs C. It seems ...
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### Searching solution for solving huge linear system in MATLAB or C

I am encountering a problem that my MATLAB code ran and an error occurs and shows that it is out of memory. My code is using finite element method to solve some complicated kind of integral equation ...
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### Complex Numbers in C Resulting in Unstable Calculation

I'm trying to perform a calculation which involves the following C-function: ...
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### Eigen-unsupported: Levenberg - Marquardt algorithm

I am using Eigen-unsupported: LevenbergMarquardt algorithm. I use this algorithm inside my model. I wrote the minimization code both in MATLAB (using fsolve) and C++ and both gave the similar results ...
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### Solving electron density function for Hydrogen and drawing in 3D

I recently stumbled upon interesting site that has interactive 3D representation of radial electron distribution (atomic orbital). here is the url: http://winter.group.shef.ac.uk/orbitron/AOs/1s/e-...
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### Performance of adding eight numbers sequentially vs. in a tree

The simplest way to add 8 numbers would be something like this, sum = one + two + three + four + five + six + seven + eight; This (in C) would add ...
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### Should I pass command line arguments to MPI_Init or not?

When writing MPI 3.0 code, should I pass argc and argv to the MPI_Init call or not, and why? ...
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### Fastest linear solver for sparse positive semidefinite, striclty diagonally dominant matrix

What is the state of the art for fastest linear solver for sparse, positive semi definite and strictly diagonally dominant matrix with N varies from ~700 to ~3000, and about a 1/16 of the matrix is ...
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### How can DFT of a two dimensional array be found using program for one dimensional DFT in C?

I have the program four1.c from Numerical Recipes in C to calculate the Discrete Fourier Transform (DFT) of a one dimensional array. I want to calculate the DFT of ...
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### Beginning Computer Programming [closed]

I was 7 years old when I learnt BASIC. Then I learnt C and Visual Basic till the age of 13. I stopped programming for 4 years continuously, and don't remember much about it now. I have lost the skill, ...
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### Looking for Runge-Kutta 8th order in C/C++

I would like to use Runge-Kutta 8th order method (89) in a celestial mechanics / astrodynamics application, written in C++, using a Windows machine. Therefore I wonder if anyone knows a good library / ...
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### C - OpenMP, MPI, Serial Program

I'm part of a Computational Science course and come from a non-programming background, so please forgive me my ignorance. I'm working on a set of code in C to numerically solve the Navier Stokes ...
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### C - OpenMP, MPI, Serial Program [duplicate]

I'm part of a Computational Science course and come from a non-programming background, so please forgive me my ignorance. I'm working on a set of code in C to numerically solve the Navier Stokes ...
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### PyOpenGL/OpenGL Generating Cosmic NBodys

I am working on a Universe Simulator. I'm stuck on creating the dark matters webs of the universe that look like this: http://www.mpa-garching.mpg.de/galform/data_vis/sim3dnew-highres.png I am ...
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### Accurate implementation of the logarithm of the incomplete Beta function in C++?

I need an accurate implementation (for use in C/C++) of the logarithm of the incomplete Beta function: $$\log \mathrm{B}(x,y;\alpha,\beta) = \log \int_x^y t^{\alpha-1}(1-t)^{\beta-1}\mathrm{d}t$$ ...